1. Field of the Disclosure
This disclosure relates generally to drilling of lateral wellbores for recovery of hydrocarbons, and more particularly to maintaining temperature of a bottomhole assembly below certain threshold temperature.
2. Description of the Related Art
To obtain hydrocarbons such as oil and gas, boreholes are drilled by rotating a drill bit attached at a drill string end. The drill string may include a jointed rotatable pipe or a coiled tube. Boreholes may be vertical, deviated or horizontal. A drilling fluid (also referred to as “mud) is pumped from the surface into the drill string, which fluid discharges at the drill bit bottom and circulates to the surface through the annulus between the drill string and the borehole. Modern directional drilling systems generally employ a bottomhole assembly (BHA) and a drill bit at an end thereof. The drill bit is rotated by rotating the drill string from the surface and/or by a drilling motor (also referred to as the “mud motor) disposed in the BHA. A number of downhole devices placed in close proximity to the drill bit measure a variety of downhole operating parameters associated with the BHA. Such devices typically include sensors for measuring: temperature, pressure, tool azimuth, tool inclination, bending, vibration, etc. measurement-while-drilling (MWD) devices (or tools) or logging-while-drilling (LWD) devices (or tools) are frequently used as part of the BHA to determine formation parameters, such as formation geology, formation fluid contents, resistivity, porosity, permeability, etc. Such devices include sensor elements, electronic components and other components that are rated to operate properly below a temperature limit, typically 150° C.
The temperature along the BHA during drilling operations, particularly in long horizontal boreholes, may be higher than the formation temperature. In long horizontal boreholes, the borehole circulating temperature (BHCT) sometimes rises above a static temperature and often above the acceptable upper temperature limit. For the purposes of the present disclosure, the term “drilling operation” is intended to include all operations in which the BHA is in the borehole. Included in such operations are situations period during which: the drill bit is drilling the borehole and the drill bit is set off the borehole bottom with or without mud circulation through the drill string and the borehole annulus. The increase in BHCT during drilling operations is at least in part attributable to the fact that the thermal equivalent of the work done downhole increases temperature of the borehole fluid, which in turn increases the temperature of the fluid circulating about the BHA and thus temperature of the BHA. Also, an increase in BHCT above static geothermal gradient increases the temperature of the formation rock near the borehole wall. This can result in increased compressive hoop stress in the borehole wall due to thermal expansion. The increased stress on the borehole wall can lead to failure of the borehole wall. Therefore, it is desirable to provide apparatus and methods that will reduce the bottomhole assembly temperature during drilling operations.
The present disclosure provides apparatus and methods that address some of the above-noted and other needs.